The central pain systems

Abstract

The central neurone systems are dealt with, which are activated by painful stimulation of the skin or are influenced by the central effects of such stimulation. Pain is a central nervous manifestation. While there is no specific peripheral receptor system for pain, that system extending from spinal posterior horn to thalamus has a close relationship with the experience of pain. Many fibres of the spinothalamic tract run to the nuclei of the reticular formation of the medulla oblongata, of the pons, and of the midbrain from which nuclei secondary connections are made with thalamus and subthalamus. Through them the reticular activating system with its arousal effects can be stimulated. Collaterals to the periaqueductal grey matter could serve as a basis for the affective reactions to pain stimuli. In the region of the thalamus a sub-division occurs (a) in a cortical pain conduction over the small celled caudal ventral nucleus (V. c. pc) which when stimulated in man results in severe pain, to the koniocortex area 3 b of the posterior central gyrus, stimulation of which scarcely ever provokes typical pain, and (b) in a subcortical pain conduction over intralaminar nuclei of the thalamus, over the nucleus limitans and perhaps over the centromedian to the outer segment of the pallidum. In order to relieve intractable pain permanently by means of thalamic coagulation it is necessary to destroy both the cortically dependent pain nuclei of the thalamus and to coagulate the nuclei responsible for subcortical pain control. — Extirpation of both II. sensory area produces no reduction of the pain.